In various systems and processes, alignment of a tool and a workpiece allows processing of the workpiece using the tool. Precision alignment of a workpiece and a tool often makes use of an alignment system. Alignment can involve moving the workpiece, the tool or both.
Examples of systems and processes in which an alignment system is applicable include lithography, photolithography, laser etching, printed circuit board masking, printed circuit board drilling, flexible circuit board manufacture, micro-machining, precision assembly, robotics, computer-aided manufacturing and other printing and manufacturing tasks.
Photolithography systems require precise alignment of a workpiece, such as a printed circuit board or a semiconductor wafer, and a photolithographic apparatus, such as a projection optics unit. As printed circuit board manufacture and semiconductor wafer processing can involve multiple layers, with each layer having a pattern to be imparted to a substrate, precise alignment of the respective substrate to the projection optics unit is performed prior to each patterning step in which an exposure image is projected on the substrate. Failure to adequately align the substrate and the pattern results in a misaligned pattern on the substrate, often resulting in rework, rejected parts or field failures due to low reliability.
Precision alignment in known photolithography systems makes use of a target alignment pattern, sometimes referred to as an alignment reticle, deposited on a substrate in a masking step. Subsequent masking steps, in which subsequent patterned layers are applied in additive processes or etched to remove in subtractive processes, or combinations thereof, rely on aligning to a previously deposited target alignment pattern, and may add further alignment patterns. Quality-control checking often includes a visual or automated inspection of the relative alignment of such deposited target patterns from multiple layers.
In certain processes it is desirable to operate on a material that is a continuous web, as may be routed over rollers. Examples of such processes include printing of newspapers, magazines, books, packaging and other articles on paper from a continuous roll, and printing of flexible substrates such as flexible printed circuit boards.
U.S. Pat. No. 7,650,839 METHOD FOR REGISTERING PATTERNS ON A WEB, to Brost et al. describes a method for registering patterns on a web that is routed over a first roller and a second roller. A registration of a pattern applied to the web is measured and provides an error signal. The error signal is used for controlling lateral and longitudinal position error, and lateral and longitudinal scale error. Independent lateral and longitudinal scale control avoids non-linear distortions. The pattern, applied by a known patterning device such as an inkjet print head, a lithographic device, a flexographic printing device, a screen printing device or a radiant energy beam patterning device, is detected by two cameras or other sensors. Scale control is implemented by changing temperature of the web or tension of the web. A lateral position of process hardware can be adjusted to control lateral position error, and timing can be adjusted to control longitudinal position error.
U.S. Pat. No. 6,753,947 LITHOGRAPHY SYSTEM AND METHOD FOR DEVICE MANUFACTURE, to Meisburger, discloses a continuously moving stage that is used in a lithography system. A metrology device measures the workpiece stage position. An alignment system aligns a mask image projected through a projection lens to a previously deposited masked pattern on the workpiece. A distorted grid is best-fitted to multiple exposure field locations to predict locations of the remaining exposure fields, and takes into account variations in X and Y magnifications, skew, and X and Y keystones. A workpiece is delivered from a workpiece storage unit to the stage. Alignment marks are imaged, a position is analyzed and an offset is measured.
Improvements in an alignment system are sought. Particularly, an improved alignment system is sought which would be usable in various systems and processes involved with various workpieces or with continuous material flow and which would be applicable in aligning a tool to a workpiece having few preprocessing steps or materials applied thereto.